1. Field of the Art
The present invention relates to a process for hydrating a nitrile thereby converting it into a corresponding amide by the action of a nitrile hydratase originated in a microorganism. More particularly, the present invention relates to a process for biologically producing an amide characterized by the microorganism used and a method for producing nitrile hydratase.
2. Background Art
A lower aliphatic amide such as acrylamide is produced by the hydration of a nitrile such as acrylonitrile, and there have been proposed many methods of hydration by the action of enzymes such as nitrilase or nitrile hydratase produced by microorganisms (see, for example, Japanese Patent Publication No.21519/87, U.S. Pat. No.4,001,081; Unexamined Published Japanese Patent Application Nos. 162193/86 and 91189/87, EPC Nos. 0188316 and 0204555; and Japanese Patent Publication Nos. 17918/81 and 37951/84, U.S. Pat. Nos.4,248,968 and 4,637,982). Such methods for biologically producing an amide have also been used commercially and have attracted attention as being advantageous processes for producing acrylamide.
Several microorganisms have already been proposed as the ones used for the process for biologically producing an amide. However, as far as the present inventors have researched, these microorganisms, although effective for the hydration of lower aliphatic nitriles, are not always effective for the hydration of aromatic nitriles. Thus, the method for producing nicotinamide by the hydration of 3-cyanopyridine exhibits too low a yield to use for commercial purposes.
The prior art to carry out the culture of microorganism in the presence of an iron ion or a manganese ion is known. This technique is utilized also in the process for biologically producing an amide, and examples for culturing the microorganisms of genus Rhodococcus in the presence of an iron ion are disclosed in Unexamined Published Japanese Patent Application Nos. 162193/86 and 91189/87.
As a result of the research conducted by the present inventors, it was found that a nitrile hydration enzyme, i.e., nitrile hydratase, originated in a bacterium of genus Pseudomonas contains Fe.sup.+++ in its active center and thus the presence of an iron ion in a culture medium is essential to the culture of the microorganism. Accordingly, it is also presumed in the case of the microorganism of genus Rhodococcus in the known examples described above that an iron ion in the culture medium for culturing the microorganism is essential to the production of a nitrile hydration enzyme.